The use of embossed plastic carrier tapes for use with surface mount components such as semiconductors including integrated circuits, contact elements or discrete electrical elements such as capacitors and resistors to facilitate automatic handling, insertion and connection to printed circuit boards or other types of substrates is well-recognized. Embossed carrier tapes are fabricated to meet standardized requirements with respect, for example, to leader characteristics, pitch, trailer characteristics and cover tape.
Embossed carrier tapes are specified, for example, in 16 mm and 24 mm sizes in the March, 1991, Standard, EIA-481-2 entitled "16 mm and 24 mm Embossed Carrier Taping of Surface Mount Components for Automatic Handling". Other tapes are specified in EIA-481-3 November of 1991, entitled "32 mm, 44 mm and 56 mm Embossed Carrier Taping of Surface Mount Components for Automatic Handling". EIA-481-1-A, August, 1994, entitled "8 mm and & 12 mm Punched & Embossed Carrier Taping of Surface Mount Components for Automatic Handling" specifies yet other tape sizes.
Notwithstanding the availability of the above noted standards, there is an ongoing need to be able to more precisely position and carry smaller and smaller components. This requires heretofore unavailable carrier tapes which can be manufactured at high speed to tighter tolerances than have been available using prior art approaches.
FIGS. 1 through 6 illustrate various deficiencies of known prior art approaches. FIGS. 1, 2 and 4 illustrate two different prior art carrier tapes. FIGS. 3 and 5 illustrate molds used to form the types of carrier tapes illustrated in FIGS. 1, 2 and 4 and in particular that of FIG. 4. FIG. 6 illustrates another form of a prior art mold usable to form tapes of a type illustrated in FIG. 4.
In FIG. 3, a prior art two-part molding system includes an upper or cover portion P1 and a lower or detail portion P2. The cover portion P1 is shown in FIG. 3 at a slight angle only for purposes of discussing the operation and characteristics thereof. In normal operation, the elements P1, P2 would exhibit relative linear motion toward and away form one another during the manufacturing process. The elements P1 and P2 cooperate to mold or emboss carrier tape T1, using a known prior art approach.
Carrier tape T1 is initially a planar flexible thermal plastic tape of a predetermined width and thickness which is positioned between elements P1 and P2 after having been heated to an appropriate temperature. Once the mold elements P1 and P2 are brought together with a section of the carrier tape T1 therebetween, air pressure can be injected via hose H1 into the cavity C1. The air pressure in the cavity C1 forces the portion of the carrier tape T1 between elements P1 and P2 into the pocket defining female molds M1, M2, M3 and M4. This, in turn, forms a plurality of carrier pockets CP1, . . . CP4 in the respective region of the tape T1.
As is clear from FIGS. 3, 4 and 5 in the prior art approach, since the carrier tape T1 is forced into the female mold elements M1 . . . M4, all of the detail present in those mold elements will be transferred to an outer surface S1 . . . S4 associated with the respective pocket CP1 . . . CP4. As clearly illustrated in FIG. 4, the respective outer surface Si is displaced away from and is not present in the component carrying pocket CPi. Similar comments apply to the carrier tapes of FIGS. 1, 2.
Because of the structure of mold elements P1, P2 the exact detail of the mold cavities M1 . . . M4, is embossed on the respective outer surfaces S1 . . . S4. Conversely, the component carrying pocket, for example CPi of FIG. 4, is formed with much less detail or definition due to not having direct contact with the mold cavities M1 . . . M4. The lack of direct contact by the mold element with the component positioning surfaces being formed limits the tolerances and precision to which those surfaces can be formed. The fact that the tolerances can not be reduced as needed for smaller parts limits the prior art technology.
In addition, as the respective regions of the carrier tape T1 are driven into the mold cavities M1 . . . M4, the thermal plastic material which makes up the tape T1 stretches. This, in turn, thins the walls of the cavity CPi and introduces wall thickness variations, which are not always of a predictable nature, into the respective cavity.
Using the prior art approach, each of the pockets formed in the carrier tape suffers from a loss of definition due to an absence of direct contact with the respective mold cavity in the block P2. Those pockets also suffer from variable wall thicknesses brought about by the molding process which may be of an unpredictable and random nature. Further, these variations are on the side of the component pocket where it is most desirable to hold the closest tolerances since it is that side of the pocket which ultimately determines the location of the product or component being carried on the tape.
Rotary molds , illustrated in FIG. 6, are also known in the prior art. In such molds, female cavities R1-1, R1-2 . . . R1-n, corresponding to the cavities M1 . . . M4 of element P2 were formed in a rotary mold element such as element R1. Carrier tape T2 would be fed across the mold element R1 at a predetermined rate, consistent with the speed of rotation of the element R1.
At the appropriate location, L1 either compressed air can be driven against the adjacent region of the tape T2 using fixture F1 and/or the respective cavity R1-i currently at the location L1 can be evacuated using evacuation conduit E1 to thereupon force-draw the relevant region of the tape T2 into the respective cavity. The rotary mold R1, as was the case with the linear mold combination P1, P2 imparts all of the detail of the respective cavity to the outside surfaces of the component carrying pocket being formed, comparable to that pocket illustrated in FIG. 4.
Using the known approaches, carrier tape on the order of 0.016 inches thick can be embossed using air pressure in a range of 30 to 100 psi and molds of the general type illustrated in FIGS. 3 and 6. This process results in component carrier pockets wherein positioning tolerances can only be held to within .+-.0.005 inches.
There continues to be a need for molds and methods which can be used to produce molded carrier tape to smaller tolerances than has heretofore been possible using the prior art approaches. Preferably such molds and methods can be configured so as to minimize in-pocket variations due to variable wall thicknesses.
It would also be preferably if such carrier tapes could be manufactured in a way that light incident thereon will be dispersed instead of reflected. Suppression of such reflections is desirable in scanning or optical monitoring systems which can used to check product or component location and contact arrangement in the carrier pocket.